1. Field of the Invention
The present invention relates to image forming apparatuses such as a copier and a printer and a cartridge detachably mountable on the image forming apparatus, and particularly to an image forming apparatus in which a residual amount of a developer can accurately be detected and a cartridge detachably mountable on the image forming apparatus.
2. Description of the Related Art
As one example of an image forming apparatus, in electrophotographic image forming apparatuses such as an electrophotographic copier and a laser beam printer, an electrophotographic photosensitive member as an image bearer is irradiated with light corresponding to image information to form a latent image, a developer is supplied to the latent image by developing means to develop the image, and further the image is transferred to a recording sheet from the photosensitive member so that the image is formed on the recording sheet.
The developing means is provided with a developer container, and the developer in the developer container is consumed by forming the image.
In such conventional image forming apparatus in which an electrophotographic image forming process is used, a process-cartridge system is employed in which an electrophotographic photosensitive member, and process means acting on the electrophotographic photosensitive member, that is, charging means and developing means are unified in a cartridge, and the cartridge is detachably mountable on a main assembly of the electrophotographic image forming apparatus. According to the process-cartridge system, since maintenance of the apparatus can be performed by a user without depending on a serviceman, operability can remarkably be enhanced. Therefore, the process-cartridge system is broadly used in the electrophotographic image forming apparatus.
In the electrophotographic image forming apparatus of the process-cartridge system, when the developer is used up, the image can be formed again by changing the cartridge. However, the cartridge has to be changed by the user, and this requires means for informing the user that the developer has been consumed, that is, a developer-amount detector.
For the developer-amount detector, in order to make it possible to know the residual amount of the developer usable for image formation in the cartridge at any time, a developer-residual-amount-pick-up part, which can pick up a signal of a developer-residual-amount level, is disposed in the cartridge or the image forming apparatus main assembly.
As one type of this developer-residual-amount-pick-up part, a flat antenna type is used. In a plane antenna, as shown in FIG. 3, a pair of conductive patterns 22, 23 are formed at a predetermined interval on a substrate 21, and the antenna is disposed, for example, in a position of the side surface of the developer container such that the antenna is in contact with the developer. When the developer in the developer container decreases, the contact area of the developer with a plane antenna 20 decreases.
When the developer is consumed, the contact area of the surface of the conductive pattern with the developer changes, and this also changes the electrostatic capacity. It is therefore possible to establish a correspondence between the residual amount of the developer in the container and the electrostatic capacity of the plane antenna. When the electrostatic capacity of the plane antenna is measured, the residual amount of the developer in the container can be known at any time.
When a constant alternating-current bias is applied to one of the pair of conductors 22, 23, the electrostatic capacity of the plane antenna 20 can be known from a current flowing through the other conductor.
In practice, even when the developer in the developer container gradually decreases, a slight amount of remaining developer sticks to the surface of the plane antenna 20. Therefore, an antenna cleaning member is attached to an agitating member disposed in the developer container, and the surface of the plane antenna is cleaned with rotation of the agitating member.
However, when the antenna surface is cleaned in this manner, an output of the plane antenna 20 fluctuates with a period in which the antenna surface is cleaned by the cleaning member. Therefore, the developer-residual-amount level is defined by taking an average value in accordance with the period, selecting a minimum value, or performing another statistical processing operation.
However, even when the developer-residual-amount-pick-up part 20 capable of picking up a signal of the developer residual amount is disposed, the value detected by the developer-residual-amount-pick-up part and the amount of the developer remaining in a developing device cannot accurately be detected in some cases.
For example, for the electrostatic capacity of the plane antenna 20, and the positional relation between two electrodes (conductive patterns 22, 23), even in a case in which there is no developer, the closer to each other the electrodes are, the larger the absolute value of the electrostatic capacity becomes, The farther from each other the electrodes are, the smaller the absolute value becomes. That is to say, the antenna output is influenced by an antenna manufacturing tolerance. When the developer-residual amount is detected only with the antenna output, the detected amount sometimes becomes far different from the actual residual amount of the developer. Moreover, because of not only the process cartridge but also the image-forming-apparatus main assembly, the detected electrostatic capacity value is caused to sometimes become different from the actual value.
Therefore, in a conventional art, when a detected electrostatic capacity value of a point at which the container is full of the developer is larger than an initially set (assumed) value, the developer-residual amount is estimated more than the actual amount. Thereby, the developer is used up before a warning is issued, and a null image is frequently formed. Conversely, when the detected electrostatic capacity value of the point at which the container is full of the developer is smaller than the initially set (assumed) value, the developer-residual amount is estimated to be less than the actual amount. In this case, even when much developer remains in the developing device, a warning indicating that there is no developer is sometimes issued. If the process cartridge is changed according to this warning, a large amount of developer is wasted.
The present invention relates to further improvement of such image forming apparatus and a cartridge which is detachably mountable on the image forming apparatus.
The present invention has been developed in consideration of the aforementioned problems, and an object thereof is to provide an image forming apparatus in which a residual amount of a developer can accurately be detected and a cartridge which is detachably mountable on the image forming apparatus.
Another object of the present invention is to provide an image forming apparatus comprising:
a developer container for containing a developer;
developer amount detecting means for detecting the amount of the developer contained in the developer container;
a memory;
read/write means for reading and writing information with respect to the memory; and
calculating means for calculating the display level of a residual amount of the developer,
wherein at least the developer container and the memory are disposed in a unit and the unit is detachably mountable on a main assembly of the image forming apparatus, and
the memory stores information indicating that the unit is new, and the calculating means calculates the display level in accordance with xe2x80x9cinformation written into the memory by the read/write means upon detecting the information indicating that the unit is new, and an output of the developer amount detecting meansxe2x80x9d.
Another object of the present invention is to provide an image forming apparatus comprising:
a unit detachably mountable on a main assembly of the image forming apparatus, the unit having a memory and a developer container for containing a developer; and
calculating means for calculating a display level of a residual amount of the developer,
wherein the memory of the unit that is unused stores information indicating that the unit is new, and the calculating means calculates the display level in accordance with a detected residual amount of the developer and a detected amount of the developer of a point at which the new information is detected.
Still another object of the present invention is to provide a cartridge comprising:
a memory; and
a developer container for containing a developer,
wherein the memory stores information indicating that the cartridge is new.
Further objects of the present invention will be apparent upon reading the following detailed description with reference to the accompanying drawings.